The present invention relates generally to an improved conveyor positioner system for flexible plastic film products, and particularly to a high speed wicketing or stacking device for handling flexible plastic film products as they are sequentially delivered in non-captive form from a web converting apparatus such as a flexible plastic film bag-making machine or the like. Bag-making machines for the fabrication of film products from polyethylene are examples of such apparatus, and are in common usage in the art.
A conveyor system to position the plastic film product, such as polyethylene bags, in correct alignment for the rotary stacking device is normally an inherent part of the bag-making apparatus. A conveyor system utilizing the Bernoulli effect to position the film product is described in co-pending application Ser. No. 909,000, filed May 24, 1978. The system disclosed in application Ser. No. 909,000 utilizes a flow of compressed gaseous fluid, such as air, beneath the plane of travel of the film product creating a pressure reduction that draws the film product to the stacker input station and positions the film product on a reliable and repeatable basis.
In certain stacking applications, a wicket pin is utilized for retention of a quantity of bags in a stack, with the bags normally having uniform perforations or holes along one of the ends, such as along an upper lip extension, for engagement with the wicket pin. Stacker apparatus which has been used in the past is disclosed in U.S. Pat. No. Re. 27,523 and U.S. Pat. No. 3,921,827, with such stacking apparatus employing a rotary hub carrying bag retaining arms for receiving the individual bags at a stacker input station for ultimate delivery onto a wicket member. As suggested in U.S. Pat. No. 3,921,827, the retaining arms of the stacker or wicketer device are provided with vacuum means for engaging the bag to be placed on a wicket member with means provided to terminate the vacuum at a given angular point in the rotary motion of the retaining arms to facilitate placement of the bag on the wicket member.
As can be appreciated, the problems encountered with handling plastic film products such as bags increases significantly as machine speed is increased. Plastic film products are exceedingly difficult to handle at high rates of speed because of the inherent flimsiness of the film material and the inherent viscosity of the ambient air. The film products become distorted and may fold or flex so that uniform pick-up and later delivery to the ultimate disposition may be adversely affected. In other words, any misalignment, folding or other anomalies in the form of the product will be reflected in adverse stacking conditions and may result in a jamming situation, damaged product, or an unattractive arrangement of finished product.
In order to assist in the correct alignment of plastic film products for placement on wicket members, to provide for adaptation of rotary stacking devices to accommodate large film products, to provide for less turbulence in the air in the production area, and to create a more energy efficient rotary stacking device, it has been found that the addition of grid-like extension members to one of the pair of work arms of a rotary stacking device is desirable.
Heretofore, rotary stacking devices have utilized either clamping means or vacuum pressure to hold a plastic film product in position on the arms of the stacker during the stacking or wicketing operation. The known stacking devices are limited as to the size of the plastic film product that may be utilized by these devices. The bag or other such product must fit within the pairs of clamps of a clamp-type system for proper operation. In a vacuum system, the distance between the arms, and therefore the size product that may be accommodated, is limited by the foil effect created by the movement of the plastic film through air. Too great a distance between the arms results in deformation of the film product between the arms during movement, and too small a separation results in overhang of the product on one of the arms with deformation or off-centering of the product occurring during movement.
It will be appreciated that conveyor and positioning systems, such as those described in pending Application Ser. No. 909,000, and vacuum pick-up systems, such as those described in U.S. Pat. No. 3,921,827, that are dependent on moving streams of air to create pressure differentials are susceptible to extraneous changes in air pressure caused by movement in close proximity to the work station. It will also be appreciated that changes in air pressure in proximity to the film products will cause off-centering or deformity of the film products themselves. These changes in air pressure and turbulence are created by the highspeed orbital movement of the arms of a rotary stacking device containing clamps or pads that present a large surface area against movement through the air of the loading and unloading zone.
The utilization of a grid-like extension member on one of the two arms of a rotary stacking device permits the use of the apparatus with varied sizes of film products without extensive modification of the apparatus or stacking system. The original spacing of the arms is retained thus reducing the foil effect of the moving film product and, by providing a support system for oversize products, distortions or off-centering caused by overhang of the film product from the arms is prevented and added stabilization for the film product is provided. The use of a grid-like extension member also serves to reduce air turbulence in the work area caused by rapid orbital movement of clamps or platens affixed to stacker arms.